In a wireless network, discovery is a process in which one or more mobile stations discover information about one or more neighboring devices. For example, the mobile stations may discover identity information, location information, etc. of the neighboring devices. There are a variety of manners in which the discovery process may be performed. In one exemplary manner, the discovery process includes periodically broadcasting a discovery signal using a discovery resource of the mobile station. The discovery signal may include the discovery information. Thus, when a first mobile station receives a discovery signal broadcast from a second mobile station, the first mobile station has discovered the existence of the second mobile station as a neighboring device and may further be aware of the discovery information related thereto.
The broadcasting of the discovery signal by the mobile stations may be transmitted as a function of a type of system on which the mobile station is operating. In a first example, the mobile stations may broadcast the discovery signal as a function of time. Accordingly, a time division multiple access (TDMA) system may be utilized in which different time slots are designated for the broadcast. In a second example, the mobile stations may broadcast the discovery signal as a function of a code. Accordingly, a code division multiple access (CDMA) system may be utilized in which a code is used for each broadcast. In a third example, the mobile stations may broadcast the discovery signal as a function of a frequency time resource (e.g., a set of subcarriers at a certain time-frame). Accordingly, a frequency division multiple access (FDMA) or orthogonal FDMA (OFDMA) system may be utilized in which a frequency band or division of frequency bands (i.e., channel) is used.
In the FDMA or OFDMA system, the dynamic mapping of a discovery channel to a physical time frequency resource (discovery resource) is called channel hopping. Channel hopping is required to achieve frequency diversity and to minimize adjacent channel interference. Frequency diversity is required to overcome the impact of frequency selectivity or to average out interference from a neighboring cell(s) through a discovery channel in which the discovery signal is broadcast. Mitigating adjacent interference is required since, in OFDMA system, a receiver listens to two or more discovery signals at the same time. Signals from different users may have leakage to adjacent channels, which cause multi-user interference or adjacent channel interference especially when the power levels from difference users are not balanced. Therefore, the channel in which the discovery signals are broadcast from respective mobile stations in the wireless network must be sufficiently diverse in the location of the physical resource to avoid or minimize such interference.
Conventional manners of transmitting discovery information based on frequency (and channels) include synchronizations, resource orthogonalization, channel hopping, etc. such that the discovery information is transmitted across multiple nodes in a resource-efficient, fast, and reliable manner with little coordination. Frequency domain channel hopping is a method to transmit the signals in wideband systems by selecting a different frequency resource among many available frequency resources. Conventionally, a pseudorandom sequence known to both transmitter and receiver is used so the intended receiver listens to the correct channel. However, this pseudorandom sequence includes drawbacks. For example, they may make any two channels collide in the same time and frequency resource; they may lack frequency diversity; they may make any two channels be adjacent relatively often than others; etc. Given the requirements of frequency diversity for discovery signals, the frequency domain hopping scheme should make any discovery resource hop over an entire bandwidth with possibly equal frequency. Furthermore, the frequency domain hopping scheme should randomize neighboring discovery channels in the frequency domain to make the period that any two discovery channels are adjacent with each other as large as possible.
Accordingly, there is a need for addressing the above noted drawbacks of conventional frequency hopping and for providing a hopping scheme that randomizes the mapping between a discovery channel and a discovery resource to mitigate the potential adjacent channel interference for achieving frequency diversity.